The present invention relates to an aircraft wing structure profiled suspension pylon.
It is known that certain aircraft comprise profiled pylons suspended from their wing structure and projecting from the pressure face thereof. Such pylons are intended for suspending devices such as engines, weaponry, fuel tanks, etc., under the wing structure.
Naturally, these pylons and the devices suspended from them give rise to disturbances in the aerodynamic flow over the wing structure and this locally results in a loss of lift and an increase in drag. These unfavorable aerodynamic effects are moreover worsened because, for structural reasons in particular, said pylons are, on the one hand, relatively wide and, on the other hand, have their trailing edge in the vicinity of the trailing edge of the wing structure, such trailing-edge proximity increasing the risks of airstream detachment.
To overcome these drawbacks, the airbus A320 has, from as early as 1986, been using a fairing for reducing the local loss in aerodynamic lift due to such a suspension pylon. A fairing of the same type (which is described, for example, in EP-A-0 432 972) is arranged in contact with the pressure face of said wing structure and extends, on the one hand, heightwise, over part of said pylon and, on the other hand, toward the rear of the wing, as a continuation beyond the trailing edge thereof. A known fairing such as this has the approximate shape of a right parallelepiped ending at the rear in a rounded-vertex pyramid. The upper surface of the fairing, projecting beyond the trailing edge of the wing structure, continues the suction face thereof and the width of said fairing corresponds to the maximum width of said pylon, which means that the lateral faces of said fairing extend the maximum-width section of said pylon rearward.
For a medium-sized airplane, this known fairing is of acceptable dimensions. However, for a large-sized airplane it is necessarily lengthy and bulky, which gives rise to heavy aerodynamic loadings exerted on said fairing in flight. This entails stiffening it, which results in a penalizing increase in mass.
Furthermore, when the wing structure has mobile trailing-edge elements, such as wing flaps, this fairing has itself to be mobile. In this case, for certain flight configurations, the fairing may find itself at least partially in the hot air jet from an engine (the temperature of which may be as high as 700xc2x0 C.), which means that it then has to be made of heat-resistant materials and designed to withstand these high temperatures and acoustic fatigue. This then results in mass constraints and additional production costs.
The object of the present invention is to overcome these drawbacks.
To this end, according to the invention, the aircraft wing structure suspension pylon, said wing structure comprising a pressure face, the rear part of which is concave and set back with respect to its front part and said pylon:
being suspended from said wing structure, projecting with respect to said pressure face of the wing structure and being profiled to comprise, between its leading edge and its trailing edge, a section of maximum width; and
being equipped with a fairing for reducing the local loss of aerodynamic lift, which:
is placed in contact with the pressure face of said wing structure and extends heightwise over part of said pylon; and
extends toward the rear of the wing structure, and continues beyond the trailing edge thereof, in the form of a projecting rear part with an upper surface in aerodynamic continuation of the suction face of said wing structure,
is noteworthy in that:
said maximum-width section of said pylon is arranged at the front of said concave and set-back rear part of the pressure face of the wing structure; and
said fairing for reducing the local loss in aerodynamic lift:
is housed, at least over most of its height, in the concavity of said rear part of the pressure face of the wing structure,
extends toward the rear of the wing structure, widening laterally in the manner of a fan, from said suspension pylon, where it has a width at least approximately equal to said maximum width thereof, as far as the trailing edge of the wing structure, where it has a width at least equal to twice said maximum width, and
comprises an underside which comes close to said upper surface, in aerodynamic continuation of the suction face of the wing structure so as to give said projecting rear part of said fairing the shape of a blade which tapers toward the rear and ends in an aerodynamic trailing edge, which projects from the trailing edge of the wing structure and extends along the latter over a length corresponding to said width of said fairing at said trailing edge of the wing structure.
Thus, by virtue of the present invention there is obtained a fairing which is flat, has small dimensions in the height direction, but a shape which is spread out along the trailing edge of the wing structure and is able to solve the abovementioned problems of the known fairing. Such a flat and spread-out shape makes it possible not only to eliminate the problems near the trailing edges of the wing structure and of the suspension pylon, but also to greatly alter the local flow of the air by encouraging the distribution of velocity at the trailing edge of the wing structure. The gain in lift achieved by the fairing according to the present invention is markedly greater than that of the known fairing. In addition, this gain in lift is more spread out across the span, because of the special spread-out shape of the fairing of the invention.
It will be noted that, in order to cancel, or at the very least to minimize, the loss in lift due to the presence of the suspension pylon and to the installation, for example the motive power unit, that it carries, one might be tempted to give said fairing a width (at the trailing edge of the wing structure) which in terms of span covers the entirety of the lift loss zone. However, if this were to be done, this width could be equal to many times the maximum width of the pylon, which would entail said fairing having large dimensions and therefore a great mass. Hence, in practice, the width of the fairing at the trailing edge of the wing structure is the result of a compromise between the gain in lift afforded by said fairing of the invention and the corresponding mass of this fairing.
It will also be noted that the tapered shape of the aerodynamic trailing edge of said fairing makes it possible to considerably reduce the length of the part of the known fairing projecting beyond the trailing edge of the wing structure for a similar order of aerodynamic efficiency. Experience has shown that that the present invention makes it possible to reduce the height of the fairing by about 80% and to reduce the length of said projecting part thereof by about 50%, with respect to this known fairing, for essentially equal aerodynamic efficiency with respect to the risk of airstream detachment at the trailing edge of the pylon and with respect to loss-of-lift problems. Such a reduction in the dimensions therefore makes it possible to avoid the mass and bulkiness drawbacks mentioned hereinabove and, in the case of a mobile fairing near to the hot jet from an engine, makes it possible to reduce the constraints on the design and the kinds of materials to use.
Advantageously, the trailing edge of said projecting rear part has an intermediate part and two lateral parts, said intermediate part being in the aerodynamic continuation of said maximum-width section of said pylon and projecting further, with respect to the trailing edge of the wing structure, than said lateral parts.
Thus, it is this intermediate part which is in the continuation of the suspension pylon, which projects the farthest with respect to the trailing edge of the wing structure so as to limit as far as possible any problems with airstream detachment and loss of lift which are due to the presence of said suspension pylon. For their part, the lateral parts of the trailing edge of the fairing make it possible to increase the gain in lift, by locally extending the chord of the wing structure, over a limited span.
At their opposite end to said intermediate part, said lateral parts of the trailing edge of the projecting rear part may gradually meet the trailing edge of the wing structure and said intermediate part of the trailing edge of the projecting rear part may be rounded and convex, whereas said lateral parts of the trailing edge of the projecting rear part may comprise a concave portion where they meet said intermediate part.
In order to improve the efficiency of the fairing according to the present invention, it has been found that it was advantageous if:
said underside of said fairing has an intermediate rib and two lateral flanks;
said intermediate rib is in the aerodynamic continuation of said maximum-width section of said pylon, ends at the rear in the form of said intermediate trailing edge part and is more in relief, with respect to said rear part of the pressure face of the wing structure, than said lateral flanks; and
said lateral flanks gradually connect said intermediate rib to said rear part of said pressure face of the wing structure while at the same time laterally forming said fan and ending at the rear in the form of said lateral parts of the trailing edge of said projecting rear part.
The fairing according to the invention may be symmetric or asymmetric with respect to the longitudinal axis of the foot of said suspension pylon.
Whatever the embodiment of the trailing edge of the fairing, it goes without saying that it is necessary to make sure that the shape of the projecting rear part thereof does not give rise to airstream detachments which would increase drag.
Furthermore, in order to avoid the projecting rear part of the fairing according to the present invention being submerged in the viscous effects of the boundary layer in the vicinity of the trailing edge of the wing structure (which would appreciably reduce the aerodynamic efficiency of said fairing), it is important that, at said trailing edge of the wing structure, the thickness of said fairing be greater than the thickness of the boundary layer of the aerodynamic flow over said wing structure.